Constituent members of a semiconductor element-manufacturing apparatus and a reaction furnace for making said constituent members

ABSTRACT

The constituent members of a semiconductor element-manufacturing apparatus which are formed by depositing a silicon carbide layer on a carbon substrate, and wherein a peak X-ray diffraction on the (200) plane of the silicon carbide layer has a half value width of 0.35° or less as measured by the C u  --K.sub.α ray used in the X-ray diffraction analysis.

This application is a continuation of application Ser. No. 421,025,filed Sept. 22, 1982, now abandoned which is a division of applicationSer. No. 162,943, filed June 25, 1980, now U.S. Pat. No. 4,424,193.

BACKGROUND OF THE INVENTION

This invention relates to the constituent members of a semiconductorelement-manufacturing apparatus such as a silicon single crystal-pullingcrucible, heater, process tube and susceptor and a reaction furnace formaking said constituent members.

Constuent members of a semiconductor element-manufacturing apparatus aregenerally known to be prepared from, for example, carbon or quartzglass. In this case, said constituent members have the surface coated,if necessary, with a silicon carbide layer by the chemical vapordeposition (CVD) method. The formation of said silicon carbide layer isintended to prevent a semiconductor material from being contaminated byundesired impurities released from a carbon or quartz glass substrate.

However, a silicon carbide layer produced by the conventional CVD methodis formed, as shown in the microscopic photographs of FIGS. 1 to 3, ofan agglomeration of fine crystals of silicon carbide (a scale given inthe photographs represents 80 microns), which represent a lowcrystallinity of silicon carbide. Therefore, the silicon carbide layerprepared by the known CVD method has the serious drawbacks that theimpurities of the substrate tend to pass through the boundary of siliconcarbide particles, and consequently, unless the silicon carbide layer ismade considerably thick, it is impossible to prevent a semiconductormaterial from being contaminated by the aforesaid impurities.

The carbon constituting the substrate of the respective constituentmembers of the semiconductor element-manufacturing apparatus has athermal expansion coefficient of 2.5 to 5.5×10⁻⁶ /°C. On the other hand,a silicon carbide to be formed on said substrate has a thermal expansioncoefficient of 4.2×10⁻⁶ /°C. Even when produced by the same process, thecarbon substrate indicates considerably wide variations in properties.For example, the thermal expansion coefficient of the carbon substrategenerally shows changes of about ±10%. Therefore, it is practicallyimpossible to establish coincidence between the thermal characteristicsof the carbon substrate and those of the silicon carbide layer. In thecase of, for example, a crucible, heater, process tube and susceptorwhich are repeatedly subjected to heating and cooling, a differencebetween the extent of thermal expansion of the carbon substrate and thatof the silicon carbide layer readily leads to the occurrence of cracksin the silicon carbide layer, particularly when said silicon carbidelayer is made considerably thick as 500 microns in order to suppress thepermeation of impurities contained in the substrate through the siliconcarbide layer. As a result, the effect of suppressing said permeation ofimpurities can not be realized at all. The growth of cracks in thesilicon carbide layer during the use of the constituent members whichresults from a difference between the thermal characteristics of thecarbon substrate and those of the silicon carbide layer is anotherserious drawback directly related to the contamination of asemiconductor material.

In consideration of the above-mentioned circumstances, the Japanesepatent publication No. 1003 (1972) set forth the constituent memberssuch as crucible of a semiconductor element-manufacturing apparatus inwhich the substrate and a layer mounted thereon were prepared from thesame material to ensure coincidence between the thermal characteristicsof both substrate and mounted layer. Said Japanese patent publicationwas intended to suppress the permeation or release of impurities in asubstrate material by thermally depositing a layer of thermallydecomposable graphite on the surface of a porous graplite substrate.However, said technique had the drawbacks that a layer of thermallydecomposable graphite was thermally deposited on the surface of a porousgraphite substrate with the axis A of the layer of said thermallydecomposable graphite set parallel with the surface of the porousgraphite substrate; the thermally deposited layer of said thermallydecomposable graphite indicated too great an anisotropy to allow for therepetitive use of the member produced; particularly the edge portion ofthe thermally deposited layer of said thermally decomposable graphitebegan to peel even in the initial stage of application of the member,thus rendering the member substantially inapplicable; and the layer ofthe thermally decomposable grappite which was considerably soft wasready to be mechanically damaged, giving rise to the occurrence ofpinholes.

The Japanese patent publication No. 26,597 (1973) proposed an attempt tomechanically improve the adhesivity of a silicon carbide layer to acarbon substrate. The proposed method comprised the steps of lettingsilicon gas flow over a carbon substrate to effect reaction between thecarbon substrate and silicon, thereby forming an intermediate layer ofsilicon carbide (SiC) prominently adhesive to the carbon substrate; andpouring a silicon-containing gas and a carbon-containing gas, therebyforming a silicon carbide layer by the customary CVD process. However,the method of the Japanese patent publication had the drawbacks thatsilicon immediately reacted with carbon; consequently unless a silicongas was let to flow over a carbon substrate uniformly and quickly, anununiform intermediate layer of silicon resulted, presentingdifficulties in effecting the uniform thermal deposition of a siliconcarbide layer in the succeeding step. Therefore, the method of theabove-mentioned Japanese patent publication was accompanied with ratherharmful effect and failed to be put to practical use.

To date, various studies have been made on the formation of a siliconcarbide layer. From the point of view that greatest importance isattached to the high purity of silicon carbide when the constituentmembers of a semiconductor element-manufacturing apparatus are produced,the widely accepted method of forming a silicon carbide layer includesthe CVD process using starting materials of high purity, and, above all,the process which involves the following reaction systems:

    SiCl.sub.4 +[H.C]+H.sub.2 (wherein, H.C. denotes hydrocarbons) (1)

or

    CH.sub.3 SiCl.sub.3 +H.sub.2                               ( 2)

A silicon carbide layer itself thermally deposited by either of theabove-mentioned processes indeed has a good purity. However, suchsilicon carbide layer is not yet freed of the serious drawbacks thatimpurities contained in a carbon substrate readily tend to permeate thesilicon carbide layer on the substrate of the member; and cracks readilytake place in said silicon carbide layer because of a difference betweenthe thermal characteristics of the carbon substrate and those of thesilicon carbide layer.

The most important reason why it is impossible, as previously described,to ensure coincidence between the thermal characteristics of a carbonsubstrate and those of a silicon carbide layer is that a startingmaterial of carbon generally has various types and its properties aregradually shifted without definite and noticeable transistion point; andeven when the same manufacturing method is applied, it is extremelydifficult to produce carbon substrates having the same properties withhigh reproducibility. With respect to, therefore, a carbon substratecoated with a silicon carbide layer, the conventional process comprisesstrictly sellecting only those carbon substrates which have preferredthermal characteristics from among a large number of produced lots. Todate, therefore, a carbon substrate has been manufactured with anextremely low yield, a factor of deteriorating the economic phase ofproducing a carbon substrate.

SUMMARY OF THE INVENTION

It is accordingly an object of this invention to provide the constituentmembers of a semiconductor element-manufacturing apparatus which preventa semiconductor material from being contaminated by impurities releasedfrom a carbon substrate.

Another object of the invention is to provide the constituent members ofthe semiconductor element-manufacturing apparatus in which theoccurrance of cracks in the silicon carbide layer of said constituentmembers is minimized even when said constituent members are repeatedlysubjected to heating and cooling for manufacture of a semiconductorelement.

Still another object of the invention is to provide a reaction furnacecapable of coating the carbon substrate with a silicon carbide layerwhich effectively suppresses the permeation of the impurities of thecarbon substrate.

To attain the above-mentioned objects, this invention provides theconstituent members of a semiconductor element-manufacturing apparatuswhich are formed of a silicon carbide layer thermally deposited on acarbon substrate, and in which the peak X-ray diffraction on the (200)plane of said silicon carbide layer has a half value width of 0.35° orless as measured by the C_(u) --K.sub.α ray used in the X-raydiffraction analysis of said silicon carbide layer. The silicon carbideconstituting said silicon carbide layer has such a high crystallinity ashas been unattainable by the conventional CVD method.

For the object of this invention, it is preferred that silicon carbidecrystal particles whose maximum width (a maximum distance between theboundaries of the adjacent silicon carbide crystal particles) is largerthan 0.15 t+5 microns (wherein t denotes the thickness of the siliconcarbide layer) should occupy more than 30% of the whole polished surfaceof the silicon carbide layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 are the microscopic photographs (a scale indicated thereindenotes 80 microns) of a silicon carbide layer deposited on a carbonsubstrate by the conventional CVD method;

FIG. 4 is the microscopic photograph (a scale given therein represents80 microns) of the silicon carbide layer formed on a carbon substrate bythe method of this invention;

FIG. 5 shows the X-ray diffraction charts of the silicon carbide layer Aof FIG. 4 embodying this invention, and the silicon carbide layers B, C,D of FIGS. 1 to 3;

FIG. 6 indicates the enlarged X-ray diffraction charts in the proximityof the peak X-ray diffraction on the (200) plane of said silicon carbidelayers A, B, C, D of FIG. 5; and

FIG. 7 is a schematic sectional view of a reaction furnace for thermallydepositing a silicon carbide layer on a carbon substrate in order toproduce the constitunt members of the semiconductorelement-manufacturing apparatus according to the method of thisinvention.

DETAILED DESCRIPTION OF THE INVENTION

A silicon carbide layer deposited on a carbon substrate to provide theconstituent members of a semiconductor element-manufacturing apparatusaccording to this invention is crystallized, as shown in the microscopicphotograph of FIG. 4 in a far higher crystallinity than the siliconcarbide layers of FIGS. 1 to 3 produced by the conventional CVD method.

X-ray diffraction analysis was carried out of the above-mentionedsilicon carbide layers A, B, C, D under the following conditions:

    ______________________________________                                        Voltage impressed on an X-ray tube                                                                      30 KV                                               Current supplied to the X-ray tube                                                                      20 mA                                               Scanning speed of diffraction instrument                                                                1/4°/min                                     Running speed of recording sheet                                                                        1/2°/min                                     Inclination angle of C.sub.u --K.sub.α                                                            1°                                           ray-generating slit                                                           Inclination angle of C.sub.u --K.sub.α                                                            0.1°                                         ray-introducing slit                                                          Inclination angle of C.sub.u --K.sub.α                                                            1°                                           ray-scattering slit                                                           Range                     1 K                                                 Scale                     1.0                                                 Time constant             1                                                   ______________________________________                                    

As a result, the X-ray diffraction analysis produced the charts of FIG.5. Reference numeral A of FIG. 5 denotes the X-ray diffraction chart ofthe silicon carbide layer of this invention whose crystal pattern isshown in FIG. 4. Reference numeral B of FIG. 5 represents the X-raydiffraction chart of the conventional silicon carbide layer whosecrystal pattern is indicated in FIG. 1. Reference numeral C of FIG. 5shows the X-ray diffraction chart of the conventional silicon carbidelayer whose crystal pattern is set forth in FIG. 2. Reference numeral Dindicates the X-ray diffraction chart of the conventional siliconcarbide layer whose crystal pattern is given in FIG. 3. Measurement wasmade of the half value widths of the peak X-ray diffraction on the (200)plane of the respective silicon carbide layers A, B, C, D from the peakX-ray diffraction patterns of FIG. 6 enlarged from those of FIG. 5. Thesilicon carbide layer of this invention denoted by the reference numeralA of FIG. 6 have a half value width of 0.33°. In contrast theconventional silicon carbide layer represented by the reference numeralB of FIG. 6 had a half value width of 0.45°. The conventional siliconcarbide layer shown by the reference numeral C of FIG. 6 had a halfvalue width of 0.93°. It was practically impossible to determine thehalf value width of the conventional silicon carbide layer indicated bythe reference numeral D of FIG. 6. In other words, the silicon carbidelayer of this invention denoted by the reference numeral A had anextremely small half value width as measured on the (200) plane. Wherethe silicon carbide layer of the invention indicated a smaller halfvalue width than 0.35° as measured on the (200) plane, then the siliconcarbide layer was found to effectively prevent impurities contained in acarbon substrate from being released therefrom.

The crystal particles of a silicon carbide layer having theabove-mentioned property of this invention are little subject to thermaldistortion W. H. Hall's formula:

    β.cos θ/λ=1/ε+η sin θ/λ

where:

β=true half value width

θ=Bragg's angle

λ=wave length of X-ray

ε=size of crystal particle

η=effective distortion of a crystal lattice

proves that a small half value width measured in the X-ray diffractionanalysis of a crystal means a small distortion of the lattice of thecrystal. In fact, even where a considerable latitude is allowed for theproperties of a carbon substrate, in other words where an appreciabledifference occurs between the thermal properties of a carbon substrateand those of a silicon carbide layer deposited thereon, it is possibleaccording to this invention to reduce the occurrence of cracks andpinholes in a silicon carbide layer when the constituent members arerepeatedly heated and cooled to produce a semiconductor element.

The above-mentioned W. H. Hall's formula further proves that a smallhalf value width determined in the X-ray diffraction analysis of acrystal not only means a small thermal distortion of the lattice of thecrystal but also a large size of crystal particles. In fact, crystalparticles in the surface of the silicon carbide layer of this inventionwhich have a maximum width larger than 0.15t+5 microns (t denotes thethickness in microns of the silicon carbide layer) occupy more than 30%of the polished surface of said silicon carbide layer as shown in the250 times magnified microscopic photograph of FIG. 4. In other words,the silicon carbide layer of this invention is formed of noticeablylarger crystal particles than the conventional silicon carbide layers ofFIGS. 1 to 3.

The silicon carbide layer of this invention preferably has a thicknessof about 20 to about 500 microns. The silicon carbide layer of FIG. 4has a thickness of 100 microns.

Description is now given of a reaction furnace of this invention forforming a silicon carbide layer on a carbon substrate. The deposition ofa silicon carbide layer is generally carried out by either of thefollowing processes:

(1) the conventional CVD method which comprises introducing raw gasescontaining silicon source and carbon source into a reaction chamber andheating the charged mass at the normal or reduced pressure; and

(2) when a substrate itself is prepared from carbon, a silicon gas isintroduced into the reaction chamber for thermal reaction with thecarbon substrate at the normal or reduced pressure.

The reaction furnace of this invention represents an improvement on theconventional method, enabling a silicon carbide layer highlycrystallized as prvieously described to be deposited on a carbonsubstrate. The reaction furnace of the invention comprises a reactionchamber surrounded by partition walls of carbon or silicon carbide; acarbonaceous vessel placed in the reaction chamber to hold silicapowder; and a heater for heating the reaction chamber. With the reactionfurnace of the invention, gases of silicon source and carbon source arenot introduced into the reaction chamber from the outside. Upon heating,reaction takes place between silica powder and the carbonaceous vesselholding said silica powder or between silica powder and carbon powdermixed therewith, thereby evolving a gas mainly comprising siliconmonoxide in the reaction chamber. This silicon monoxide gas is broughtinto contact at high temperature with a carbon substrate placed in thereaction chamber. As a result, a silicon carbide layer is formed on thesurface of the carbon substrate.

Description is now given with reference to FIG. 7 of the constructionand operation of a reaction furnace embodying this invention. FIG. 7indicates the main part of the reaction furnace. This main part of thereaction furnace is set in a furnace body (not shown) formed ofrefractory material. The reaction chamber 1 is surrounded by acylindrical partition wall 2 formed of carbon and/or silicon carbide.Provided outside of the cylindrical partition wall 2 is a cylindricalheater 3 for heating the reaction chamber to a temperature of 1500° to1900° C., preferably 1650° to 1750° C. The heater 3 itself shouldpreferably be built of carbon or silicon carbide. With the thisembodiment, a second partition wall 4 is disposed between the firstcylindrical partition wall 2 and heater 3. It is possible to providesuch a multipartition wall or single partition wall. A carbon substrate(not shown) which is to be chemically processed is held in the reactionchamber 1 by proper engagement means provided on the innermost partitionwall. A carbon vessel 5 is mounted on a rest board 6 fixed at the bottomof the reaction chamber 1. A silica powder 7, if necessary silica powderand carbon powder, is filled in said carbon vessel 5. The partitionwalls 2, 4 are erected on the rest board 6. The upper end of the heater3 is covered with a water-cooled cap 8. When the partition wallprotrudes from the upper end of the heater 3, then the cap 8 may bemounted on the upper end of said partition wall. The substantiallycentral part of the cap 8 is provided with an exhaust port 9communicating with an exhaust device (not shown), for example, a vacuumpump.

With the reaction furnace constructed as described above, a carbonsubstrate tube chemically processed is set in the reaction zone of thereaction chamber 1 apart from a vessel 5 holding silica powder 7, andthereafter the heater 3 is supplied with power, and a vacuum pump (notshown) is actuated. Then the carbon vessel 5 and silica powder 7received therein are brought into contact with each other under heat,mainly evolving silicon monoxide gas. This gas is conducted into thereaction zone of the reaction chamber 1 which is kept at a temperatureof 1500° to 1900° C. by the heater 3 and is decompressed to 100 to 0.1torr by the vacuum pump. A silicon carbide layer is chemically depositedon the surface of the carbon substrate to a considerable depth and inthe highly crystallized form. Therefore, the silicon carbide layerformed by the method of this invention has the advantages that thesilicon carbide layer has a high adhesivity to the carbon substrate,high crystallinity and uniform quality; even when deposited with athickness of about 100 microns, the layer is sufficiently impervious toimpurities released from, for example, a carbon substrate; the peakX-ray diffraction on the (200) plane of the layer has a small half valuewidth; the layer is formed of large crystal particles and consequentlyis prominately adapted to produce the constituent members of asemiconductor element-manufacturing apparatus.

This invention will be more fully understood from the examples whichfollow.

EXAMPLE 1

A silicon carbide layer was deposited on the surface of a carbonsubstrate with a thickness of 100 microns to make four types ofsusceptors used in the step of epitaxial growth in the manufacture of asemiconductor element. The peak X-ray diffractions on the (200) plane ofthe silicon carbide layers of these susceptors respectively indicated0.33°, 0.35°, 0.36° and 0.39° as measured by the C_(u) --K.sub.α ray. Asilicon layer was epitaxially grown from high purity silicontetrachloride with a thickness of 10 microns by the hydrogen reductionmethod on a substrate of silicon single crystal sapported on each of theabove-mentioned susceptors. The resistances of the epitaxially grownsilicon layers were determined by the 4-needle method to compare theproperties of the susceptors. The results are set forth in Table 1below.

                  TABLE 1                                                         ______________________________________                                                Half value width of peak                                                      X-ray diffraction on the                                                      (200) plane of the silicon                                                                      Resistance of an                                    Sample  carbide layer of each                                                                           epitaxially grown                                   No.     susceptor         silicon layer                                       ______________________________________                                        1       0.33°      over 50 Ω · cm                       2       0.35°      over 45 Ω · cm                       3       0.36°      20 to 35 Ω · cm                      4       0.39°      10 to 30 Ω · cm                      ______________________________________                                    

As seen from Table 1 above, silicon layers epitaxially grown by means ofsusceptors (samples Nos. 1 and 2) whose surface was coated with asilicon carbide layer whose peak X-ray diffraction had a half valuewidth of 0.35° and less indicated high resistance and high purity. Thereason for this is that an epitaxially grown silicon layer was notcontaminated by impurities contained in a carbon substrate, and thesilicon carbide layer effectively prevented the impurities from beingreleased from the carbon substrate. In contrast, silicon layersepitaxially grown by means of susceptors (samples Nos. 3 and 4) whosesurface was coated with a silicon carbide layer whose peak X-raydiffraction had a larger half value width than 0.35° showed a smallresistance, and were contaminated by the impurities of the carbonsubstrate which permeated the silicon carbide layer.

EXAMPLE 2

A silicon carbide layer was deposited on a carbon substrate with athickness of 100 microns to make four sets of the so-called hot zoneparts such as a silicon single crystal-pulling crucible, heater and heatshield. The silicon carbide layer of each member of the four sets of thehot zone parts was polished with a diamond paste until the surface ofsaid silicon carbide layer was smoothed out. In this case, with a firstset of the hot zone parts, silicon carbide crystal particles whosemaximum width was over 20 microns (=0.15×100 microns (layer thickness)+5microns) occupied 0% of the polished surface of the silicon carbidelayer. With a second set of the hot zone parts, the silicon carbidecrystal particles occupied 10% of the polished surface. With a third setof the hot zone parts, the silicon carbide crystal particles accountedfor 30% of the polished surface. With a fourth set of the hot zoneparts, the silicon carbide crystal particles accounted for 40% of thepolished surface. The respective sets of the hot zone parts were used topull up an N type silicon single crystal having a diameter of 80 mm anda specific resistivity of 20 to 25 Ω.cm. The carbon content of therespective pulled up silicon single crystals was determined inaccordance with the method specified in the ASTM-F123-70T, the resultsbeing set forth in Table 2 below.

                  TABLE 2                                                         ______________________________________                                                  Percentage areas                                                              of the polished                                                               surfaces occupied                                                             by silicon carbide                                                            crystal particles                                                   Nos. of samples                                                                         having a maximum                                                                             Carbon content of                                    of hot zone                                                                             width larger than                                                                            a silicon single                                     parts     20 microns     crystal                                              ______________________________________                                        5          0             7.2 × 10.sup.16 atoms/cm.sup.3                 6         10             5.5 × 10.sup.16 atoms/cm.sup.3                 7         30             1.6 × 10.sup.16 atoms/cm.sup.3                 8         40             0.7 × 10.sup.16 atoms/cm.sup.3                 ______________________________________                                    

Table 2 above shown that to produce a silicon single crystal having asufficiently low carbon content for practical application, more than 30%of the polished surface of a silicon carbide layer should be occupied bysilicon carbide crystal particles whose maximum width (that is, adistance between the boundaries of the adjacent silicon carbide crystalparticles) is larger than 20 microns, in case the silicon carbide layerhas a thickness of 100 microns. Where silicon carbide crystal particleshaving a maximum width larger than 20 microns occupy 0% or 10% of thepolished surface of the silicon carbide layer, then the silicon carbidelayer has a high carbon content, causing an impurity of carbon releasedfrom the carbon substrate to exert a harmful effect on the manufactureof a semiconductor element.

EXAMPLE 3

A silicon carbide layer was deposited with a thickness of 100 microns onfour carbon boards each measuring 100×100×15 mm. The respective carbonboards were heated to 1200° C. in 5 minutes, and kept at the temperaturefor ten minutes, and thereafter naturally cooled to room temperature. Inthis spalling test, it was determined how often the carbon boards had tobe repeatedly heated and cooled, before pinholes or cracks were firstappeared in the silicon carbide layer deposited on the carbon boards.Table 3 below shows a number of heating-cooling cycles required for thefirst growth of pinholes or cracks in the silicon carbide layers, halfvalue widths of peak X-ray diffractions on the (200) plane of thesilicon carbide layers and the percentage areas of the polished surfacesof the silicon carbide layers occupied by silicon carbide crystalparticles having a maximum width larger than 20 microns.

                  TABLE 3                                                         ______________________________________                                                         Percentage areas                                                              of the polished                                                                            Number of heating-                                               surfaces occupied                                                                          cooling cycles                                                   by silicon car-                                                                            required for the                                Nos. of          bide crystal first growth of                                 samples                                                                              Half value                                                                              particles having                                                                           pinholes or                                     of hot width of  a maximum width                                                                            cracks in the                                   zone   peak X-ray                                                                              larger than 20                                                                             silicon carbide                                 parts  diffraction                                                                             microns      layers                                          ______________________________________                                         9     0.33°                                                                            40           150                                             10     0.35°                                                                            30           145                                             11     0.36°                                                                            15            60                                             12     0.39°                                                                             0            50                                             ______________________________________                                    

The samples Nos. 9 and 10 were shown to have an effective life 2 to 3times longer than the samples Nos. 11 and 12.

EXAMPLE 4

A silicon carbide layer was deposited on a carbon substrate in areaction furnace constructed as shown in FIG. 7. A carbon cylindricalpartition wall 2 of the reaction furnace had an inner diameter of 80 cmand a height of 180 cm. A carbon vessel 5 was placed on a rest board 6.2500 g of silica powder 7 was received in the carbon vessel 5. A carbonsubstrate was set on the partition wall 2 by means of a hook about 60 cmabove the silica powder 7. The interior of a reaction chamber 1 washeated to about 1700° C. by a heater 3, kept at said temperature for 240minutes, and also decompressed to about 0.5 torr by a vacuum pump. Asilicon carbide layer was deposited on the carbon substrate with athickness of 80 microns. The half value width of a peak X-raydiffraction on the (200) plane of the silicon carbide layer was 0.340 asmeasured by the C_(u) --K.sub.α ray used in said X-ray diffractionanalysis. A microscopic photograph shown that silicon carbide crystalparticles whose maximum width was larger than 20 microns occupied 45% ofthe polished surface of the silicon carbide layer.

This invention produces the constituent members such as a crucible,heater and susceptor of a semiconductor element-manufacturing apparatusby depositing on a carbon substrate a silicon carbide layer which ishighly crystallized and whose crystals themselves are little subject tothermal distortion. Even where, therefore, the constituent members areused at high temperature, the silicon carbide layer effectively preventsthe impurities of the carbon substrate from passing through the siliconcarbide layer. Even where the constituent members are repeatedlysubjected to heating and cooling during the manufacture of asemiconductor element, the growth of pinholes or cracks in the siliconcarbide layer can be effectively suppressed. Moreover, the siliconcarbide layer tightly adheres to the carbon substrate by being deeplyset therein. Through, therefore, the carbon substrate and siliconcarbide layer have different thermal properties, the generation ofpinholes or cracks in the silicon carbide layer can be minimized.Consequently, it is possible to apply carbon substrates falling within abroad range, regardless of a difference between their properties. asilicon carbide layer produced by this invention has the above-mentionedexcellent properties. Even when therefore made considerably thinner thanpossible in the past, for example, deposited on a carbon substrate witha thickness of about 100 microns, the silicon carbide layer of thisinvention can prevent a semiconductor material or element from beingcontaminated by impurities released from the carbon substrate.

What we claim is:
 1. A method for manufacturing a constituent member ofa semi-conductor element-manufacturing apparatus, said methodcomprising,(1) placing (a) a carbon substrate of the constituent memberand (b) a carbonaceous vessel containing a powder comprising silica orsilica and carbon, in a reaction chamber surrounded with partition wallsmade of carbon, silicon carbide or a mixture thereof, (2) heating thereaction chamber to heat the carbon substrate, the carbonaceous vesseland the powder to a temperature of 1500° to 190° C. to cause theevolution of a gas comprising silicon monoxide and to cause a reactionbetween the carbon substrate and the silicon monoxide, thereby formingon at least one surface of the carbon substrate a silicon carbide layerhaving a half value width of 0.35° or less as measured by C_(u) --Kαrays in x-ray diffraction analysis of the (200) plane of the siliconcarbide layer.
 2. The method of claim 1, wherein the heating step iscarried out at a temperature of from 1650° to 1750° C.
 3. The method ofclaim 1, wherein the reaction is carried out under an atmosphere ofreduced pressure.